Advanced 3-D Graphics: GNU Maverik&mdash;a VR Micro-Kernel

What we have gained is the flexibility to plug together quite
different applications within a single VE framework, without
compromising performance. That is a gain, but seems to be at the
expense of having the application (and application programmer) do
all the hard work. However, because Maverik is a
framework into which things can be plugged
with little performance loss, it is easy to provide commonly useful
facilities and objects to get many applications off the ground. For
example, Maverik is distributed with libraries of common geometric
primitives, cones, cylinders, teapots, an animated avatar, sample
graphics file parsers, navigation facilities, 3-D math functions,
quarternion codes, stereo, 3-D peripheral drivers for head-mounted
display and 3-D mice (see Figure 7) and so forth). If these are
useful, then you use them as a good starting point. If they are
not, then you provide your own objects and algorithms, perhaps
refining the samples provided.

Figure 7. Immersive Editing

This makes it fairly straightforward to get started using the
system. In practice, this gives three levels of increasingly
sophisticated use.

Using the default objects and algorithms provided.
Used this way, Maverik looks like a VR building package for
programmers. The tutorial documentation for the system leads one
through the building of an environment with behaviour, collision
detection and customized navigation.

Defining your own classes of objects. This is where
you benefit from application-specific optimizations that you could
supply by providing your own rendering and associated callbacks.
The tutorial gives an example of this, and the supplied
demonstration applications make extensive use of the techniques.
Unfortunately, the offshore platform example uses commercially
sensitive data, so cannot be supplied with the distribution.

Extension and modification of the Maverik kernel.
Rendering and navigation callbacks are one set of facilities that
can be customized. For the adventurous, more of the Maverik core
functionality is also up for grabs: for example, alternate culling
strategies, spatial management structures and input device support.
But this still takes place within the context of a consistent
framework that seems to make it easy to plug different parts
together.

The real test for Maverik as a research vehicle is how well
it allows such pieces to fit into the overall puzzle. The hope is
that it will make the task of building VEs “as hard as it should
be”, avoiding the feeling that one's efforts are mostly spent
“fighting the system”. So far, given a little familiarity with
the approach, this looks very promising.

Figure 8. Navigation Algorithms

Recent Maverik developments include a novel force-field
navigation algorithm to guide participants around obstacles, and an
algorithm for probing geometry ahead of a user to test whether it
can be climbed—for example, ladders and steps (see Figure 8).
These algorithms integrate into Maverik, but at the time of this
writing are released as separate beta sources for testing.

What You Can't Do with Maverik

Maverik has no support for audio or video within it. You will
need to add your favourite mechanism for those yourself.

Maverik is a single-user VE micro-kernel. It does not include
any assistance for running multiple VEs on different machines for
sharing a world between people. To do that, you would need to
synchronize the VEs yourself across the network. For just
navigating around a shared VE, that's not so hard. Running a system
with many users across wide area networks with multiple VEs,
applications, interaction and behaviour is a more complex
challenge. It's a challenge we are working on now with a
complementary system that uses Maverik. We aim to release what we
have on that under the GNU GPL license later this year.

We are very keen to know how well these ideas work, or don't
work, for other people—particularly those with experience of
graphics programming. That way, we get to understand more about
this whole area. Feedback should be addressed to
maverik@aig.cs.man.ac.uk.

Adrian West
(ajw@cs.man.ac.uk) lectures on
computer science at the University of Manchester, U.K. He is part
of the Advanced Interfaces Research Group, working on systems
architectures for distributed virtual environments.